Converting lumens to PAR/PPF

[Anonymiss]

Diply asked about this, so I'm just going to dive right in...

PAR: Photsynthetically Available (or Active) Radiation. All radiation with a wavelength of 400nm to 700nm.

PPFD: Photosynthetic Photon Flux Density. A way to measure PAR. It's the number of photons of light falling on a given area in a given amount of time, and its units are micromoles per meter square per second (µmol m-2 s-1).

Lux: A measure of illuminance, measured in lumens per square metre.


Now, a given light source will produce a certain amount of its output as PPFD. This amount can be related directly to illuminance by way of a multiplier, and, importantly, is constant for each source type*.

Here are the multipliers to convert illuminance in Lux to PPFD for some common light sources:

Source                 Multiplier
Sunlight               0.0185
Fluorescent (Grolux)   0.029
Metal Halide           0.0141
Fluorescent (865/840)  0.0135
High Pressure Sodium   0.0122

Figures provided by Apogee Instruments.

So, we can multiply the Lux value by the multiplier in the above table to find the PPFD in µmol m-2 s-1.


Worked example:

60 cm x 60 cm space (0.36 m²)
250 Watt HPS lamp (33,200 lumens)

Lux = (total lumens) / (total area in square metres)
    = 33,200 / 0.36
    = 92,222

PPFD = Lux x factor
     = 92,222 x 0.0122
     = 1,125

What level of PPFD is good? I don't know, but I imagine that, like everything in this game, "More!" is probably the answer**. The proper information is almost certainly out there though.

As a reference, direct sunlight at midday, with a Lux value of about 100,000, will provide a PPFD of around 1,850 µmol m-2 s-1.


There's also another measure of PAR, and that's YPF (Yield Photon Flux) PAR. It's weighted more to the plant response curve, and the red end of the spectrum, than PPFD and so is probably a better measure for growing purposes, but I don't have any conversion factors.


Finally, here's a table showing the PPFD for a few lamp types and sizes:




*For suitable values of 'constant'. It's mostly constant, but may vary with specific or specialist lamps.
**There probably is a maximum upper limit, and the law of diminishing returns will probably start to take effect before that limit is reached.

[teutonic]

is there any corelation between
radiation with a wavelength of 400nm to 700nm.

and the 2700k of red 6400k for blue ? Ta for any info

[Diply]

Thanks you for this anonymiss..
Wow this is complicated, firstly heres a conversion calculator for most bulbs (but not LED) which uses the figures mentioned above. (i think)

LINK

I can't find a simple PAR-PPFD to LUX or rather LUX to PPFD for LED bulb, partly because they are so variable but also because the PAR changes exponentially the bulbs height from the plant.



there are some LED sales sites that give par conversions for their lights , but these are not household LEDS!.
Example
LINK which do take account of height.



I did find an excellent article explaining why it is so complicated!
LINK


Finally my head started to expand and throb and was on the verge of exploding so I had to stop.

[Anonymiss]

is there any corelation between
radiation with a wavelength of 400nm to 700nm.

and the 2700k of red 6400k for blue ? Ta for any info

Is this what you're looking for? These are the emission spectra for a couple of fluorescent lamps (Philips MASTER TL5 HE 28W). I don't have details for 6400K, but the 865 graph is for 6500K, which is pretty close.



Not mentioned in the table above is the multiplier for 2700K sources, and I don't have one, but for a 3000K it's 0.013.

Thanks you for this anonymiss..
Wow this is complicated, firstly heres a conversion calculator for most bulbs (but not LED) which uses the figures mentioned above. (i think)

LINK

I can't find a simple PAR-PPFD to LUX or rather LUX to PPFD for LED bulb, partly because they are so variable but also because the PAR changes exponentially the bulbs height from the plant.

there are some LED sales sites that give par conversions for their lights , but these are not household LEDS!.
Example
LINK which do take account of height.

I did find an excellent article explaining why it is so complicated!
LINK

Finally my head started to expand and throb and was on the verge of exploding so I had to stop.

Some good finds there, Diply, thank you.

The "PAR changes exponentially with the lamp height" is true for all lamps, not just LED. It's down to the fact that the lumens drop off according to the inverse-square law thing (twice the height, one-quarter the illuminance; half the height, four times the illuminance). But, and I know this sounds wrong at first, I don't think it's relevant here. The reason the illuminance drops off is because the area illuminated increases as the lamp gets further away. But we're assuming that all the light (i.e. every lumen emitted by the lamp) hits the canopy, regardless of the height. That's why I did the (lumens / canopy area) bit. If we wanted to standardise it we could use a canopy area of 1 m² which would give us a 'total PPF by lamp type' value, or something, and that's pretty much what I did in the table.

I think that one of the reasons that things are different, in terms of PAR/spectrum, for LEDs is that they are narrow-band sources. I'm pretty sure tha a single LED only emits a single wavelength, with multi-colour devices being built of three discrete RGB sources, and white is, I think, made using a blue (or UV?) diode which excites a phosphor (or other chemical) to emit white light. Not every white LED is the same, just like not every fluorescent lamp is the same, and the choice of phosphor (or phosphor-blend) will determine the actual colour temperature and the spectrum that makes up that particular CT, just as it does in fluorescents.

We have fairly well defined colour temperatures of 2700K, 3200K, 400K, etc. for fluorescent lamp, and each of those temperatures is likely to have similar emission characteristics for any two lamps. We may have the same CTs in LED, but different LEDs may use different wavelengths to achieve those CTs.

Specialist LED grow lights do it differently though. They omit the white-emitting diodes and focus on building panels using diodes with emisson spectra of the desired wavelengths. This should make them more efficient as there's no wasted light (unusable by the plants), and no losses in the phosphor. I suppose that this means that they could theoretically reach 100% PAR, which is, I guess, the Holy grail of plant lighting.

[Diply]

The "PAR changes exponentially with the lamp height" is true for all lamps, not just LED.

Of course ...I should have thought of that..

We have fairly well defined colour temperatures of 2700K, 3200K, 400K, etc. for fluorescent lamp, and each of those temperatures is likely to have similar emission characteristics for any two lamps. We may have the same CTs in LED, but different LEDs may use different wavelengths to achieve those CTs.

Interesting.
Here are the bands/colour temps, for my LED's and one thing, I think is true is that they are very narrow, as you suggested.

4w 3200K - 3500K
5w 3300K-3500K
9w 5500-6000K

With LEDs emitting different wavelengths, the only accurate way of truly measuring PPFD would be with a quantum meter in my specific space...?

thanks again Missy for following up on this.

[teutonic]

yer. I guess Im trying to understand what 2700k and 6400k is exactly. i bet the k stands for kelvin - which i'll have to go wiki now lol. so its a color temperature. ?

found the answer but its tuff
http://www.3drender.com/glossary/colortemp.htm

[Diply]

Hmmm interesting..

[Anonymiss]

yer. I guess Im trying to understand what 2700k and 6400k is exactly. i bet the k stands for kelvin - which i'll have to go wiki now lol. so its a color temperature. ?

found the answer but its tuff
http://www.3drender.com/glossary/colortemp.htm

Yep, that's exactly what it is.

A colour temperature in K is the colour of the light that would be emitted by a black object which has been heated to that temperature.

To convert K to °C, subtract 273 (it's actually 273.15, but I don't think that 0.15 degrees is going to make much difference here). So, 6,400K = 6,127°C.

With LEDs emitting different wavelengths, the only accurate way of truly measuring PPFD would be with a quantum meter in my specific space...?

Unless you can get the Lux to PPF factors, then yes, sadly.

thanks again Missy for following up on this.

You're welcome. I think that it's an interesting subject, and I've been meaning to post this for a while now. Your post was the spur that finally made me get around to actually doing it.

[seymour-buds]

buds grown under l.e.d lights are better than hps grown buds simply because they are grown in better enviroment of light, hps light only focuses on a certain part of the par spectrum but a flowering plant will use other spectrums outside of the hps range which is where l.e.d lights offer the ability to do that, dont get me wrong im not saying that you cant do that with hps lights but it would mean hanging different lights around your plant in order to achieve that effect

i need no convincing on l.e.d technology as a replacement for hps lights and its clear to see why a 300 watt l,e,d panel will match the par output of a 750 watt hps , my biggest concern is the full spectrum that people are trying to aim for

l.e.d lights will not have a problem producing a full spectrum with an array of l.e.d lights and with the emergence of plasma lights which are also full spectrum i have to ask the question is full spectrum lights really the way forward ??

plants will only use the light provided in the par range and anything outside of that range is wasted light, with the speed at which l.e.d has come on in the last couple of years and the arrival of plasma i really wanna see both these lights sources go head to head

people still wanna argue the fact that hps is still the industry standard grow light but trust me hps is dying a very slow death

[teutonic]

.. that's exactly what it is. A colour temperature in K is the colour of the light that would be emitted by a black object which has been heated to that temperature.

Thats blown my mind lol. Is there a real temperature difference in light ?